The present invention relates to a catheter probe, more particularly to a catheter probe comprising a magnetic nuclear resonance spectrometer arrangement capable of characterising and monitoring the local flow rate of a physiological fluid as well as its chemical composition.
Nuclear magnetic resonance is based on the following known principle. All atomic nuclei with an odd atomic mass or an odd atomic number (like hydrogen for example) possess an intrinsic nuclear magnetic momentum. Without entering the details, one can consider that this momentum is generated by the rotation of the proton around the nucleus. When a NMR active nucleus is placed in a static magnetic field, this momentum can take two different orientations. The momentum may take either an orientation parallel to the magnetic field or an antiparallel orientation relative to the magnetic filed. Considering a population of hydrogen atoms immersed in the same static magnetic field, the number of atoms having a parallel orientation is slightly greater than the number of atoms having an anti-parallel orientation. This is due the fact that the parallel orientation is energetically more favourable. The passage from the parallel state to the anti parallel state occurs when the atoms absorb electromagnetic energy at a given frequency called the resonance frequency. This resonance frequency depends on the nucleus of the atom and on the intensity of the static magnetic field. A magnetic nuclear resonance apparatus works by analysing the signal emitted during the transition from the excited state (anti-parallel) to the state of equilibrium (parallel). The nuclei are placed in a high intensity static magnetic field and then exited with an electromagnetic wave having a frequency corresponding to the resonance frequency. When the return to the equilibrium state occurs, a signal having the same frequency as the excitation signal (resonance) is generated and can be measured thanks to an antenna.
The resonance detection may occur either at the stage of excitation, by measuring the energy absorption by scanning a range of frequency or when the atoms return to the state of equilibrium. In the later, one measures the electromagnetic signal emitted by the magnetic momentum returning to their equilibrium position. If other atoms than hydrogen atoms are present in the solution to be characterised, the spin of their electrons will generate a magnetic field at the microscopic level. Thus the hydrogen atoms are submitted to the static magnetic field generated by the NMR device to which is superposed locally the magnetic field generated by the electrons. This will alter the resonance frequency with a signature specific to the environment of the hydrogen atoms within the solution to characterise. Nuclear magnetic resonance spectroscopy is based on this principle and is mainly used for two different kind of applications, namely for biochemical analysis in laboratories and in magnetic resonance imaging spectroscopy. In laboratories, nuclear magnetic resonance spectroscopy is usually performed at very high magnetic field intensity ( greater than 10 Tesla) to reveal the atomic structure of molecules. In contrast magnetic resonance imaging spectroscopy (MRIS) is performed with standard MRI equipment at lower filed intensity (around 1.5 Tesla) to reveal the composition of the tissues environment at molecular level.
It is also possible to gather information related to the flow of a liquid by analysing the signal returning to the equilibrium state after a resonant excitation. This signal has a decrease, which is characteristic when the liquid is static, and a faster decrease when the liquid is in movement. This is due to the fact that part of the excited atoms will leave the detection volume of the antenna. This technique also used in magnetic resonance imaging spectroscopy devices.
Chronic monitoring of specific chemical compounds in a body fluid as well as gathering information relative to the flow rate of a fluid within the human body is a key in many areas of medicine, this is particularly true for brain metabolites monitoring in traumatic patient or for monitoring the flow rate of the cerebrospinal fluid in a shunted hydrocephalic patient. The known techniques for monitoring the concentration of specific chemical compounds in a physiological fluid are usually achieved invasively either by techniques that require taking samples of the fluid (dialysis, . . . ) or by inserting probes in the targeted fluid/tissue (micro dialysis, blood gas analysis.) These techniques involve either a puncture for each sample to analyse or a catheter line to be left in place for the duration of the monitoring. Known invasive catheter probes are mainly targeted to specific analytes such as O2, CO2, glucose or lactose. Micro-dialysis is the only invasive technique that is versatile, but a continuous flow of buffer solution circulating in the catheter and solution sampling for off-line analysis is needed. The later technique can be considered as pseudo-continuous monitoring but is rather difficult to implement (requires regular sampling by qualified operator and one specific reagent per targeted analyte).
Other non-invasive techniques such as magnetic resonance imaging spectroscopy are rather expensive and do not permit a continuous monitoring. Moreover, concerning the flow rate assessment, there are currently no known devices to perform these measurements in situ.
The aim of the present invention is to remedy the aforesaid drawbacks. A mini-invasive nuclear magnetic resonance spectroscopy catheter probe having a permanent magnet, an electronics circuit, and an excitation coil connected to the electronics circuit and disposed within the probe achieves this goal.
Further features and other objects and advantages of this invention will become clear from the following detailed description made with reference to the accompanying drawings illustrating in a schematic and non-limiting way two embodiments of a nuclear magnetic resonance spectrometer probe according to the invention.